window folder preview and icon

my window version is win 11, i bought when i was win 10 and upgraded to 11 . but ..................i just wanted to see extended image on thumbnail preview of folder( i mean, folder preview images are halfly covered up by yellow folder so that i cannot see that image very well, since i process lots of image this was very important) so i followed this video


but i failed to change correctly even though i followed same thing(...his result having image previews but i ended up dont having any preview)........ so i found this very later

and then i want to follow this tutorial to change my preview again, but may be due to previous perturbation , not working at all ,,,,, any help would be appreciated . i follow bunch of youtube video but that did not restore to default folder icon setting. frustrating

i just want to change as totally default setting but it seems whatever i tries , never returning to default .....and folders are sometimes blacked out. i hope if i can change back to default,,....then try that simple latter video that i posted so that i could change eventually...............( i found some alternative software out there but what i want to do is batch changing or increasing image area(rather than just covered by folder)) i think window should have this by default but why this is so hard? sticking whole day and only stumble onto weird result keeps me frustrated